The invention relates to gas separation devices with gas contacting means and more particularly such devices with pneumatic reverse flushing means for media cleaning.
There are various gas separation devices employing pneumatic reverse flushing means for cleaning the gas separation media.
Examples of some such devices, commonly called bag houses employing filter bags as the gas contacting means, are shown in U.S. Pat. Nos. 3,394,532 issued on July 30, 1968 to H. Oetiker; 3,377,783 issued on Apr. 16, 1968 to H. T. Young; 3,499,268 issued on Mar. 10, 1970 to J. Paush; 3,606,736 issued on Sept. 21, 1971 to R. M. Leliaert et al; 3,798,878 issued on Aug. 18, 1972 to J. Pausch; 3,726,066 issued on Apr. 10, 1973 to D. G. Colley et al; 3,874,857 issued on Apr. 1, 1975 to D. H. Hunt et al; and 3,877,899 issued on Apr. 15, 1975 to R. P. Bondy et al.
Baghouse filter devices have worked well for many applications, but of course, they do not fulfill the need for efficient gas separation in all applications. For example, baghouse filter devices are particularly well suited for removing material from a gas stream where the material tends to pack together in a cake on the filter media or has an adhesive affinity for the filter media. This is because the caked material can be easily removed by shaking the bag filter or reverse flushing with high energy gas which distorts the bag and breaks up the caked material. Baghouse type devices are also suited for applications where the physical size of the housing is of no concern because they are typically very large due to the fact that the filter bag must themselves be large.
Another known filtering device similar in structure to the baghouse type includes a housing for enclosing filters, but uses pleated cylindrically shaped filters in place of the tubular bag filters. This type of device is cleaned by injecting a high stream energy gas stream into the filter in a direction counter to the flow of dirty gas to be cleaned. Because the cylindrical filter is rigid and, therefore, not really distortable, it is not particularly well suited for removing material from a gas stream which cakes together or has an adhesive affinity for the filter media. However, the pleated construction of the cylindrical filter increases the surface area of filter media which can be put in a given space compared to the surface area of filter media in the same space provided by tubular bag filters. Therefore, the housing enclosing the pleated cylindrically shaped filters can be smaller than a baghouse device enclosing filter bags of the same filter media area.
Many factors must be considered in designing a filter. In addition to the desirability of having as much area of filter media in a given volume as possible, it is also important to maintain a uniform velocity of gas across the filter media; to maintain a uniform gas velocity over the face of the filter, and to maintain a uniform pressure drop across the filter over the face of the filter.
The baghouse filter devices and houses employing pleated cylindrical filters known to me do not satisfy the additional factors mentioned above concerning uniform gas velocities and pressure drops.
Therefore, there is a need for a filter device having a reverse flushing feature which satisfies these additions factors.
Furthermore, the known filter devices mentioned above employing reverse flushing means for cleaning the filter media typically require directing a jet stream of high energy cleaning gas, such as air, into each filter bag or pleated cylindrical filter. In order to effectively carry out the reverse flushing function venturi nozzles are usually located at the open end clean gas outlet of each filter bag or pleated cylindrical filter for accelerating and distributing the high energy jet stream. This translates into a proliferation of venturi nozzles, at least one for each filter bag or cylindrical filter. These venturi nozzles and their necessary mounting hardware, adds to the cost of manufacturing and maintaining the equipment.
Therefore, a need exists for a filter device having a reverse flushing means which minimizes the need for a large number of venturi nozzles.
Still further, in the known filter devices mentioned above, each filter bag or pleated cylindrical filter is attached to an aperatured plate which divides the filter house into a clean gas chamber and a dirty gas chamber. Each filter bag or pleated cylindrical filter is open at its open end to a different one of the apertures in the apertured plate to establish gas flow communication between the clean gas plenum and the downstream or clean air side of the filter bag or cylindrical filter. Necessarily, seals must be used at the attachment of each filter bag or cylindrical filter to the apertured plate to prevent leakage of dirty gas into the clean gas chamber between the interface of the filter element and apertured plate. All seals eventually deteriorate and fail, therefore, each area that must be sealed represents a source of potential leakage. Thus, the requirement for a seal at each filter element to apertured plate connection means not only a manufacturing expense, but also an expense in maintenance.
Therefore, a need exists for a filter device having a reverse flushing means which minimizes the number of seals needed to prevent dirty gas from by-passing the filter element.